1. Field of the Invention
This invention relates to an electrophotographic photosensitive member, a process cartridge having the electrophotographic photosensitive member, and an electrophotographic apparatus.
2. Related Background Art
In recent years, copying machines and printers (electrophotographic apparatus) having applied electrophotography have come into wide use. These chiefly employ lasers as light sources. As the light sources, semiconductor lasers are used taking account of cost and the size of electrophotographic apparatus.
At present, semiconductor lasers used chiefly have its oscillation wavelengths of as long as 650 to 820 nm in wavelength. Accordingly, development and research have been put forward on electrophotographic photosensitive members having a sufficient sensitivity to such long-wavelength light. Recently, development and research are also being put forward on electrophotographic photosensitive members having a sufficient sensitivity to short-wavelength semiconductor lasers in order to achieve higher resolution.
Azo pigments and phthalocyanine pigments are very effective as charge-generating materials having sensitivity in such a long-wavelength region up to a short-wavelength region. Azo pigments having specific structure are disclosed in, e.g., Japanese Patent Applications Laid-open Nos. 59-31962 and 1-183663. Also, as the phthalocyanine pigments, oxytitanium phthalocyanine and gallium phthalocyanine have superior sensitivity characteristics, and their various crystal forms have ever been disclosed in, e.g., Japanese Patent Application Laid-open Nos. 61-239248, 61-217050, 62-67094, 63-218768, 64-17066, 5-98181, 5-263007 and 10-67946.
Japanese Patent Application Laid-open Nos. 7-128888 and 9-34149 also disclose that, in order to overcome problems in phthalocyanine pigments, they are used in combination with specific azo pigments.
However, such electrophotographic photosensitive members making use of azo pigments or phthalocyanine pigments have superior sensitivity characteristics as stated above, but on the other hand have had a disadvantage that photocarriers formed tend to remain in the photosensitive layer to tend to cause variations in potential as a sort of memory.
The mechanism of this phenomenon has not been ascertained, and is presumed as follows: For example, in the case of an electrophotographic photosensitive member having a multi-layer type photosensitive layer separated functionally into a charge generation layer and a charge transport layer, electrons left in the charge generation layer move to the interface between the charge generation layer and the charge transport layer for any reason. Also, in the case of an electrophotographic photosensitive member having an intermediate layer and a conductive layer, electrons left in the photosensitive layer (charge generation layer) move to the interface between the photosensitive layer (charge generation layer) and the intermediate layer or to the interface between the intermediate layer and the conductive layer for any reason. Such carriers enhance or lower the barrier properties against hole injection in the vicinity of the interface.
When actually used as an electrophotographic photosensitive member, the former case in which electrons collect at the interface between the charge transport layer and the charge generation layer appears as a decrease in light-area potential or residual potential at the time of continuous printing. For example, where the photosensitive member is used in a development process in which the part of dark-area potential is made to serve as non-development part and the part of light-area potential as development part (what is called a reversal-development system), which is widely used at present in laser beams printers, the areas to which the light has been applied at the time of earlier printing come high in sensitivity. Hence, what is called ghost may conspicuously appear which is a phenomenon that, when a whole-area white image is printed at the time of next printing, the part of the earlier printing looms in black (hereinafter xe2x80x9cpositive ghostxe2x80x9d).
In contrast, the latter case in which electrons collect at the interface between the intermediate layer and the conductive layer appears as an increase in light-area potential at the time of printing. Where the photosensitive member is used in the reversal-development system, the areas to which the light has been applied at the time of earlier printing come low in sensitivity. Hence, what is called ghost may conspicuously appear which is a phenomenon that, when a whole-area black image is printed at the time of next printing, the part of the earlier printing looms in white (hereinafter xe2x80x9cnegative ghostxe2x80x9d).
Of these phenomena, the negative ghost often appears at the initial stage of printing, and the positive ghost during continuous printing.
This phenomenon is remarkable especially in electrophotographic photosensitive members having the intermediate layer as an adhesion layer of the photosensitive layer (charge generation layer). Especially in an environment of, e.g., low temperature and low humidity, the charge generation layer and the intermediate layer may come to have a high volume resistance to electrons, and hence the electrons tend to come full in the charge generation layer to very tend to cause the phenomenon of ghost. There has been such a disadvantage.
Japanese Patent Application Laid-open Nos. 2001-66804 and 2001-290293 also disclose that a carixarene compound is used in order to prevent such ghost.
However, for the achievement of much higher image quality and color image formation required in recent years, it is desired to better prevent in every environment the image quality from deteriorating due to the phenomenon of ghost, and it is desired to much better prevent the image quality from deteriorating especially in a severe-condition low-temperature and low-humidity environment and as a result of running.
An object of the present invention is to solve the above problems to provide an electrophotographic photosensitive member which has a high sensitivity, has a high sensitivity especially in the semiconductor laser wavelength region, and also can form images having less image defects such as ghost, not only in a normal-temperature and normal-humidity environment but also in a low-temperature and low-humidity environment; and a process cartridge and an electrophotographic apparatus which have such an electrophotographic photosensitive member.
As a result of extensive studies, the present inventors have discovered that the above problems can be solved when a carixarene compound, in particular, a carixarene compound having specific structure is used in the photosensitive layer.
More specifically, the present invention is an electrophotographic photosensitive member comprising a support and a photosensitive layer provided thereon, wherein the photosensitive layer contains a carixarene compound having structure represented by any one formula selected from the group consisting of the following formulas (1) to (5). 
wherein Y1 to Y4 each independently
represent xe2x80x94CHxe2x95x90Nxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Nxe2x95x90Nxe2x80x94 or xe2x80x94N(O)xe2x95x90Nxe2x80x94, and Ar1 to Ar4 each independently represent a substituted or unsubstituted aromatic hydrocarbon ring or a substituted or unsubstituted aromatic heterocyclic ring, provided that a case in which all the Y1 to Y4 are xe2x80x94Nxe2x95x90Nxe2x80x94 and all the Ar1 to Ar4 are the same is excluded. 
wherein Y1 to Y5 each independently
represent xe2x80x94CHxe2x95x90Nxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Nxe2x95x90Nxe2x80x94 or xe2x80x94N(O)xe2x95x90Nxe2x80x94, and Ar1 to Ar5 each independently represent a substituted or unsubstituted aromatic hydrocarbon ring or a substituted or unsubstituted aromatic heterocyclic ring, provided that a case in which all the Y1 to Y5 are xe2x80x94Nxe2x95x90Nxe2x80x94 and all the Ar1 to Ar5 are the same is excluded. 
wherein Y1 to Y6 each independently
represent xe2x80x94CHxe2x95x90Nxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Nxe2x95x90Nxe2x80x94 or xe2x80x94N(O)xe2x95x90Nxe2x80x94, and Ar1 to Ar6 each independently represent a substituted or unsubstituted aromatic hydrocarbon ring or a substituted or unsubstituted aromatic heterocyclic ring, provided that a case in which all the Y1 to Y6 are xe2x80x94Nxe2x95x90Nxe2x80x94 and all the Ar1 to Ar6 are the same is excluded. 
wherein Y1 to Y7 each independently
represent xe2x80x94CHxe2x95x90Nxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Nxe2x95x90Nxe2x80x94 or xe2x80x94N(O)xe2x95x90Nxe2x80x94, and Ar1 to Ar7 each independently represent a substituted or unsubstituted aromatic hydrocarbon ring or a substituted or unsubstituted aromatic heterocyclic ring, provided that a case in which all the Y1 to Y7 are xe2x80x94Nxe2x95x90Nxe2x80x94 and all the Ar1 to Ar7 are the same is excluded. 
wherein Y1 to Y8 each independently
represent xe2x80x94CHxe2x95x90Nxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Nxe2x95x90Nxe2x80x94 or xe2x80x94N(O)xe2x95x90Nxe2x80x94, and Ar1 to Ar8 each independently represent a substituted or unsubstituted aromatic hydrocarbon ring or a substituted or unsubstituted aromatic heterocyclic ring, provided that a case in which all the Y1 to Y8 are xe2x80x94Nxe2x95x90Nxe2x80x94 and all the Ar1 to Ar8 are the same is excluded.
The present invention is also a process cartridge which integrally supports the above electrophotographic photosensitive member and at least one means selected from the group consisting of a charging means, a developing means, a transfer means and a cleaning means, and is detachably mountable to the main body of an electrophotographic apparatus.
The present invention is still also an electrophotographic apparatus comprising the above electrophotographic photosensitive member, a charging means, an exposure means, a developing means and a transfer means.